Nope, she is the reason mc and fmc around each other, she let them meet and hand out. So yes she is the wingwoman, and she's the one who dictates the pace of their romance, she constantly makes opportunities for them, gives them time and space.
Well, it was a wrong decision to bring this back story, manga could have been better without it, all that happened fmc could explain at some point with a few words in a single chapter without all this pointless tragedy.
She is an embodiment of what almost every guy wants, Amane on the other hand is a perfect match for mc, that's why most of us prefer the harem route, and for now, the author aiming for it.
Mate it's 6 chapters and MC is already acting as a side character, if fmc hadn't taken his hand then she followed his sis it could be over already. The author should stop gay baits and make it clear that fmc is straight or I drop this, ch1-2 where golden, serialization chapters suck so far 5/10...